Adsorption von Sauerstoff, Kohlenmonoxid und Äthylen auf der Pt(111)-Fläche

Steininger, H.

Book/Report

FZJ-2018-01817

Adsorption von Sauerstoff, Kohlenmonoxid und Äthylen auf der Pt(111)-Fläche

Steininger, H. (Corresponding author)FZJ*

1982
Kernforschungsanlage Jülich, Verlag Jülich

Jülich : Kernforschungsanlage Jülich, Verlag, Berichte der Kernforschungsanlage Jülich 1763, 92 p. (1982)

Please use a persistent id in citations: http://hdl.handle.net/2128/17679

Report No.: Juel-1763

Abstract: High-resolution electron energy loss spectroscopy (EELS) and temperature programed thermal desorption spectroscopy (TPDS) were applied in studying adsorption of oxygen, carbon monoxide and ehtylene and reaction processes of ethylene and ethylene coadsorbed with atomic oxygen and hydrogen, respectively, on Pt(lll). Pt(111)/O$_{2}$: At about 100 K oxygen is found to be adsorbed in a molecular form with the axis of the molecule parallel to the surface as a peroxolike species, that is the OO-bond order is about 1. At saturation coverage ($\theta^{mol}$ = 0.44) a ($^{3/2}_{0}$ $^{0}_{3/2}$) R 15$^\circ$ diffraction pattern is observed. The sticking probability S at 100 K as a function of coverage passes through a maximum at $\theta$ = 0.11 with S = 0.68. The shape of the coverage dependenceis characteristic for adsorption in islands. Two coexisting types of adsorbed oxygen molecules with different 00-stretching vibrations are distinguished. At higher coverages a spespecies with $\nu$-00 = 875 cm$^{-1}$ is dominant. With decreasing oxygen coverage the concentration of a type with $\nu$-00 = 700 cm$^{-1}$ is increased. The dissociation energy of the 00-bond in the species with $\nu$-00 = 875 cm$^{-1}$ can be estimated to 0.5 eV from the frequency shift of the first overtone. When the sample is annealed oxygen partially desorbes at ~ 160 K, partially dissociates and orders into a (2x2) overlayer. Below saturation coverage of molecular oxygen dissociation takes place already at 92 K. Atomically adsorbed oxygen occupies threefold hollow sites with a fundamental stretching frequency $\nu$-0Pt = 470 cm$^{-1}$. In the non-fundamental spectrum of atomic oxygen the overtone of the E-type vibration is observed, which is "dipole forbidden" in EELS asa fundamental. Pt(lll)/CO: Upon adsorption around 100 K at low coverages (e $\lesssim$ 0.33) spontaneously ordered overlayers of CO, not observed before, have been found. At higher coverages the superstructures exhibit a substantial disorder at low temperatures, but get transformed into well ordered structures withdefined diffraction patterns if the sample is annealed and subsequently cooled down again. The structures have been characterized according to the binding types of CO by their vibrational spectra taken with EELS. Up to a coverage of about 0.17 CO is exclusively linearly bonded in on-top sites. At coverages above 0.17 bridge sitesare occupied in addition. At 100 K the adsorbate exhibits an island structure. [...]

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